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School me on Return Fuel Regulators

4K views 38 replies 8 participants last post by  dragking 
#1 ·
I just received my On3 fuel hat and regulator and I have an concern with the design of the regulator that I hope people can confirm or correct my suspicion concerning the Return Port size.

With all the talk about needing to make sure the fuel return line is large enough to return the fuel under cruise RPM shouldn't the return port be fairly large? This regulator comes with -10 threads but the actual port diameter is only .140 diameter. If running dual 340 pumps does the excess fuel that the engine doesn't use actually flow through this tiny port? If so what's the point of running a -8 or -10 line back to the tank?

The return port is on the bottom, correct?

Convince me this port is large enough to warrant a -8 return line.

ks
 

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#2 ·
dont know much about those regulators.
Normal convention, return is on the bottom.

The 9950-boost is a fantastic regulator for doing the speed limit to the grocery store.
I switched from the 340's and 9925-boost to the 4303 & 9950. When I called MP and told them I was thinking of keeping the 9925, I sure got an ear full.

Give magna fuel a phone call. It was an interesting phone call for me.
 
#4 ·
The fuel line and every fitting is like a resistor. If the flow rate is below turbulence, it is pretty linear with pressure.

There are online calculators that calculate pressure drop with distance. I think Goodyear or Gates has a good one. For example my car is perfectly OK with a 1500-2000 HP capable pump with only a #10 hose feed and a #6 hose return for the long lengths front to rear, and some smaller hose and fittings for short lengths. The return can be small because the differential pressure, is from rail pressure to ambient pressure. With 35 psi rail (under vacuum) there is a 35 psi delta on the return, which allows my #6 to flow enough to keep pressure at 35 or less. I think when I tested it, it would pull down to 25 or 30 on the rails.

Regulators traditionally, because of design, are fairly small flow areas in the valve area. It is a short length where cross section is small, so the fuel simply speeds up in that area. As long as it isn't going too turbulent and developing too much pressure differential, it will be OK.
 
#5 ·
Regulators traditionally, because of design, are fairly small flow areas in the valve area. It is a short length where cross section is small, so the fuel simply speeds up in that area. As long as it isn't going too turbulent and developing too much pressure differential, it will be OK.
A few people from another forum are measuring their regulators to see what the return hole diameter measures. Based on what I've seen I can't see where a -10 return line is warranted on a regulator with a .140 diameter return hole.

The one I received from On3 is an Areomotive regulator p/n 13101 – A1000-10.

ks
 
#6 ·
I discovered that the return ports can be different sizes depending on the regulators. For example the more costly Magnafuel 9950 is designed for higher HP cars uses a 3/8" hole for the return port and I think this is what I want to go with. Maybe (probably?) I don't need this large of return hole with the fuel system staged but I would rather be safe than sorry so I'll send this one back.

ks
 
#7 ·
Your thinking is correct, and you can probably drill that one out a bit. There is no point in running a return line larger than -6 with that regulator. I was on the edge of overwhelming my fuel regulator with a 340lph in tank, and since that one started running out of fuel, I put in a 450lph Walbro that completely overwhelms the regulator. Idle pressure won't go below 78 psi when the alternator's fully charging. I did a little testing and found a quarter ohm, 100w resistor was not quite enough to drop the idle psi to normal (and it got really hot), so I wired 4 1.5 ohm 100 watt resistors in parallel and put them on a heatsink for .38 ohm, 400 watt resistor. I'll be installing my "module" as soon as I get a chance - any day now.

Here's what it looks like:



One relay is for powering the pump through the resistors (low voltage), another for bypassing the resistors (full voltage) and the third is for turning on my A/W intercooler pump. FWIW, I first tried a 40 amp PWM module for the pump without success. Dunno why it didn't work. It works on a lower current motor just fine. Then I found out the resistor dropping idea is what OEMs use (Nissan, et al). Seems primitive, but it's easy.
 
#8 ·
Alex, wouldn't you rather have a FPR that can handle the fuel pump or pumps, rather than reducing the current/power that reach the pump(s)?

This should concern a bunch of people who have fuel supplies way past OEM flow levels and typical regulators. I'm planning a dual 255lt/hr system myself, and obviously it'll need a different FPR. I like the TFS injector rails, but hadn't thought about the FPR yet.

Kevin, that tiny FPR outlet does bother me too, it's interesting that it seems that the hole is part of the regulator function. I'd have guessed at an 8AN return for your level of fuel flow, but I bow to the experts who have run that high power level for real, and for a long time.

You guys are dealing with some subjects that don't get a ton of attention on forums. I like hearing about it.
 
#10 ·
Alex, wouldn't you rather have a FPR that can handle the fuel pump or pumps, rather than reducing the current/power that reach the pump(s)?
I thought about this for a bit before choosing the path I did. I street drive this car mostly, and continuously circulating massive amounts of fuel is supposed to heat up the fuel. I have nothing but anecdotal data to confirm that. Since this is a technique used by OEMs in high-powered cars that have warranties, it must have some logic behind it. Even on pumps that draw less.

This is a .74 ohm EVO factory fuel pump resistor:



I need about half of that resistance. It should actually help with pump life, too.


Alex, I'm guessing that once you get the electronics done you'll be getting a different regulator that can handle the bypassed fuel?
ks
No. For the reasons I explained above and I'm really digging my regulator packaging. This thing is intended for a Toyota or Isuzu or something (many import regulators look the same):





It'd be hard to improve upon that packaging, and it's NHRA legal (not firewall mounted).

When I was looking into this exact issue a few months back, there was another point that was made - having an 1/8" orifice is not nearly as restrictive as having a 5' long piece of 1/8" ID tubing. The math got surprisingly complicated quickly, so eventually I just said, "F it." Which is unusual for me, so take that for what it's worth.
 
#9 ·
Alex, I'm guessing that once you get the electronics done you'll be getting a different regulator that can handle the bypassed fuel?

I find it strange that nobody has ever thought about this and actually looked into the design of the regulators before blindly buying one. People are buying what they feel are correct simply based off of what the advertised specs are and the MFR's are screwing us to some degree. I researched regulators for weeks and all I could find are the "fitting/port sizes", ie -6, -8, -10, etc. But the fitting size has absolutely no correlation to how large the drilled holes are that the fuel has to flow through. Case in point are the pics I posted above. The advertised port sizes are a -10 but you can clearly see that the return hole is nowhere near that size at .140 diameter and this spec is not advertised anywhere. Even some suppliers have no clue what's going on. I Specifically asked about this and I was told that it would flow a lot b/c it was a -10 port. Now I have to pay to ship it back and a 20% restocking fee b/c it won't work for my needs.

ks
 
#12 ·
I didn't measure it, but here's a chart:



The regulator I have is preset to 49 psi. If the chart is accurate, it looks like current draw is about 16 amps.
 
#16 ·
I hope so. Even if I have to drop down to three resistors (.5 ohms, 300 watts) if I need more voltage drop.

If it doesn't work, I guess I'll look into the magnfuel regulator. $200 for a regulator just feels wrong, you know? It's like paying $500 for a belt tensioner.
 
#17 ·
Keep posting any details of what you learn and do. I'm always up for learning new things, and if there's a better way, it's good to see it sooner than after my version is done. I'm slow so mine will surely be six months or more before I get to my fuel tank project.
 
#18 ·
I'm a geek about getting data - you know I'll report back, good, bad or indifferent.

Speaking of which, I was able to sneak out for a 10 minute drive tonight. The resistor/full voltage trigger is temporarily wired to a toggle switch - when I switch on the IC pump, the fuel pump gets full voltage.

Going through the resistors, idle fuel pressure was right at 50 psi. Flip the toggle, and it shoots up to 78 psi. After a 10 minute drive, the resistors measured 133 degrees Fahrenheit and the heatsink's definitely working.

Not sure what those resistors can handle temp-wise (anyone know? Tom?), but I think they'll be fine.

Initial testing looks promising.
 
#20 ·
It's not difficult - you'd easily grasp it if you took a little time, no doubt. I can draw up a schematic for you if you want; just literally connect the dots one at a time.
 
#21 ·
How much total current is flowing through the 4 parallel resistors, or how much voltage drop is across them?

Are you sure they are in parallel pairs? Not series parallel?
 
#22 ·
Don't let the look of the wiring fool you - they are indeed all parallel. It was a concession to solid wire and the fact that my barrier strips have two screws each.

Using this calculator:

Voltage Divider Calculator - RapidTables.com

I get a voltage drop of 4.2 across the resistors and 9.3 across the pump at 13.5 volts, assuming the pump is drawing 16 amps (pump @ .84 ohms).

Thoughts on power resistor max temps?
 
#23 ·
Don't let the look of the wiring fool you - they are indeed all parallel. It was a concession to solid wire and the fact that my barrier strips have two screws each.

Using this calculator:

Voltage Divider Calculator - RapidTables.com

I get a voltage drop of 4.2 across the resistors and 9.3 across the pump at 13.5 volts, assuming the pump is drawing 16 amps (pump @ .84 ohms).

Thoughts on power resistor max temps?
Yeah, that's what I'm wondering about, the heat created and the power being consumed to reduce pump function.

I'd also like to know the practical limits of the common regulators used with return style fuel rails, or the ones mounted in the lines. If I could choose one that isn't overpowered(in normal driving) by a 255lthr pump on a 332 hitting 550hp, I'd be happy with that.
 
#25 ·
Thanks, that's what I've thought, but the posts here and recently made me wonder where that threshold is. Mine will always be a street vehicle, an SUV for nice things/fun, never dirty work(I have two others for that). So if I can do the twin 255 pumps right(wire the switch and label it and the pump locations inside the tank), then I can easily figure out which pump has to be replaced if it ever comes to that.

I don't yet want to cut a hole in the floorboard, but I did last week see the best version of that done for a 91-01 Explorer. Brian1 on the EF forum fabricates anything in real steel super well, and he made a plate(L-shaped) that fit perfectly and has a large seal around it. I could like that, because the hole is very large at the back of the rear seat floor. Dropping a fuel tank is no fun.
 
#26 ·
I run an Aeromotive Eliminator fuel pump with -12 feed line up to the engine compartment, Y off to dual -8 lines to the front of the fuel rails, -8 out of the back of the fuel rails to the Aeromotive 13101 regulator and a -6 return line to the tank. No issues making over 900 whp. Fuel pressure is spot on.
 
#27 ·
That sounds great Kevin. To me, it looks like your feed lines and fuel rails are excellent, and the only questions are the balance of the sizing and flow capacities of the pump versus the regulator and return line. I would prefer to have all of the lines more than adequate, and let the pump, regulator, and fittings be the limiting factors. It sounds like you are there but for questioning the return line size. Given your power level I would have made the return AN8 just to be sure it was enough.

But you guys are experts compared to my thoughts, and observing. Thanks for your sharing and thoughts, and allowing me to brain storm with you.
 
#28 ·
I'm running a 340lph pump with stock return line. If the fuel pressure doesnt creep up at idle then I dont see why I would need a bigger return line. I'm using the least amount of fuel at idle so that would be the most amount flowing down the return line..
 
#30 ·
The return line can be much more restricted than the feed, because the feed has to maintain pump pressure at high flow rates with minimal pressure drop.

The return can have a pressure drop of full idle rail pressure at bypass flow.

So on one line, the feed, we worry about developing a few pounds of delta at full pump flow. On the return, all we care about is if at idle (minimum rail pressure) the return can flow the pump excess back at rail (maybe 32-35psi?) to zero pressure from end to end on that line. 30 psi delta can push a lot of fuel through a small hole.
 
#32 ·
FWIW, Tom, I have a dumb question that's always bothered me. Let's say we have a pump that draws 15 amps at 12 volts. That means the motor is presenting .8 ohms of resistance (ignoring all the dynamics therein). And we want to drop a few volts off that pump, so we put a .2 ohm resistor in parallel with the pump. The pump is now turning a little slower because of reduced voltage, but are we not drawing less current total? .2 ohm + .8 ohm = 1 ohm; and at 12 volts, that's 12 amps - less than the original 15 right? The pump's only using 9.6 amps and the resistors 2.4, right? (this might be where I start going off base). Coincidentally, the pump's only dropping 9.6 volts while the resistors 2.4 volts (12 amps and 12 volts now).

Without the resistor, the pump was pulling 180 watts (12 volts x 15 amps). With the .2 ohm resistor in series, the pump is now only pulling 92 watts (9.6 volts x 9.6 amps) - only about half of what it was before, and the resistor is pulling 5.76 watts (2.4 x 2.4).

Where did I go wrong? It seems way off to go from a total load of 180 watts to less than 100 by only adding a .2 ohm resistor...
 
#33 ·
FWIW, Tom, I have a dumb question that's always bothered me. Let's say we have a pump that draws 15 amps at 12 volts. That means the motor is presenting .8 ohms of resistance (ignoring all the dynamics therein). And we want to drop a few volts off that pump, so we put a .2 ohm resistor in parallel with the pump. The pump is now turning a little slower because of reduced voltage, but are we not drawing less current total? .2 ohm + .8 ohm = 1 ohm; and at 12 volts, that's 12 amps - less than the original 15 right?
Brush type electric motors have some odd characteristics. They can be non- linear with supply voltage or load.

An efficient motor will not limit current via winding resistance. It limits current by generating a counter EMF in the armature. The armature acts like a generator as it spins, generating an opposing voltage. That opposing voltage subtracts from the supply voltage until loss resistance and the voltage difference set the run current.

This is why, when locked shaft or under heavy load, current goes way up. This is also why starting current is so high. A typical efficient motor might draw 5-10 times the start current as run current when on a stiff voltage source. It does this because only "copper resistance" sets zero speed current, and armature counter EMF is zero volts. This means the full supply voltage is across the static resistance.

When it spins up, the internal voltage subtracts from the supply voltage to make a new lower effective potential across that fixed resistance. At some speed it all reaches equilibrium.

Another thing also happens. Some motors depend on forced liquid or air flow for cooling. When slowed they cool less, so they *might* get warmer.

Shaft loading also comes into play. It can make current increase with decreased voltage. That makes heat increase as voltage is reduced, since dissipative resistance is constant.

This is why you should measure the run current and source voltage (battery) feeding the resistor/pump combo. If you know the source voltage and value of series external resistance along with voltage across that resistance, then you know pump motor heat dissipation, resistor dissipation, pump running voltage, and everything else.

Just assuming the motor resistance based on full speed run current does not work.
 
#34 ·
Update and Question:
I got the new regulator installed and the fuel lines all run. The return line is plumbed to the bottom of the regulator.

With key ON and engine OFF the pump turns on and pumps fuel but there is a LOT of fuel returning back to the tank which seems backwards. With engine OFF there is no vacuum to pull the check ball off the seat to allow fuel to return to the tank.

Is this correct?

ks
 
#35 ·
Tom - thanks for the reply; I'll study it when I don't have a headache (seriously - gotta be this storm droppng hail on us).

Kevin - That's normal. Since fuel in liquid form isn't compressible, once the regulator's pressure is reached, all the remaining fuel gets bypassed and returns to the tank. The system should hold pressure for a good long while after you shut it off too. If pressure starts to drop soon after power off, either the pump's check valve is leaking or you have a leak somewhere.

BTW, put my car on the dyno recently, and the pump control module above works like a charm. Just FYI.
 
#39 ·
reason i ask is i too have been looking into the regulator interface. my 13101 will not hold pressure [ although could be pump too] a magnafuel 4303. your thread started me wondering too about regulators. so i started doing some research this week. aeromotive states in their directions for installing a 13101 that it will not hold pressure because it is not made to seal well enough to hold pressure, saying that oems have to hold pressure to meet emissions, most aftermarket regulators do not hold pressure. so i am with you are we being fed a tub of s--t? what are you using for a pump? my system can take a couple seconds of prime to hit 40 but soon as pump shuts off its 0. thinking about making a change myself.
 
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